Acceleration of vulcanization by means of nu-mono-tertiary-alkyl-thiazoline-2-sulfenamides



'nonyl, tert-decyl, tert-undecyl and tert-dodecyl.

United States atent ACCELERATION F VULCANIZATION BY MEANS OFN-MONO-TERTIARY-ALKYL-THIAZOLINE-Z- SULFENAMIDES Edward L. Carr, Akron,Ohio, assignor to The Firestone Tire & Rubber Company, Akron, Ohio, acorporation of Ohio No Drawing. Application December '7, 1953, SerialNo. 396,761

6 Claims. (Cl. 260 788) This invention relates to the vulcanization ofrubber or the like by the use of a new class of accelerators.

This application is a continuation-in-part of my copending applicationSerial No. 90,772, filed April 30, 1949, now abandoned, which was acontinuation-in-part of my application Serial No. 586,039, filed March31, 1945, now abandoned.

An object of the invention is to provide an improved process ofvulcanizing a rubber or synthetic rubber. Another object is to provide avulcanizable rubber composition capable of rapid vulcanization atcustomary rubber curing temperatures, but free from the danger ofsetting-up during factory processing operations. The above and furtherobjects will be manifest in the descrip tion of the invention whichfollows.

The new class of accelerators of this invention possesses the followingformula:

wherein R is a tertiary alkyl radical containing from 4 to 12 carbonatoms. The invention includes thiazoline-2- sulfenamides of the abovestructure in which R is tertbutyl, tert-amyl, tert-hexyl, tert-heptyl,tert-octyl, tert- The tertiary-butyl, -octyl and -dodecyl radicals arepreferred because of their ready availability.

The following examples are given to illustrate the new class ofaccelerators and methods by which they can be synthesized.

EXAMPLE 1 Preparation of N-tert-butyl-thiazoline-Z-sulfenamide A flaskcontaining 45 grams of tert-butylarnine was stirred and cooled to 0 C.During one hourthere was added with stirring 335 ml. of 1.79 molarsodium hypochlorite solution, keeping the temperature of the mixture at0 to C. To the resulting mixture there was added over a 2 hour period200 ml. of a 3 molar solution of the sodium salt of Z-mercaptothiazolinewhile the temperature was maintained at 0 to 5 C. The cooling bath wasthen removed, the mixture was stirred an additional to minutes and thenpoured over a liter of ice and water with stirring. After the ice hadmelted, the fine, white precipitate was filtered and washed on a Buchnerfunnel until the washings were neutral. The separated product wasdissolved in a mixture of 150 ml. 95% ethyl alcohol and 100 ml. water atreflux temperature, and the solution was allowed to cool andcrystallize. The separated, white crystalline product was dried overpotassium hydroxide in a vacuum desiccator. Melting point 101- 103 C.Analysis:

F CC

EXAMPLE 2 Preparation of N-tt-0ctyl-thiazoline-2-sulfenamide A l-liter3-necked flask was equipped with an agitator, thermometer and droppingfunnel. A quantity grams) of tt-octylarnine was placed in the flask andcooled to 0 C. by means of a cooling bath. During 75 minutes there wasadded 335 ml. of a 1.79 molar solution of sodium hypochlorite, thereaction temperature being maintained at 0 to 5 C. The mixture appearedmilky during addition of the hypochlorite. To the resulting mixturethere was added over a period of 2 hours 200 ml. of a 3 molar solutionof the sodium salt of 2-mercaptothiazoline while the contents of thefllask were keptat 0 to 5 C. A soft, white solid separated and floatedto the top of the reaction mixture. Thereafter the mixture was stirredan additional hour without the cooling bath, during which time thetemperature of the mixture gradually rose to 20 C. The reaction mixturewas then poured into a liter of ice and water, the ice was allowed tomelt and the water was poured off of the precipitated solid product. Thelatter was washed several times by decantation with ice water, and thenwas recrystallized from a mixture of 200 ml. of ethyl alcohol and 65 ml.of water. The white needles were dried over potassium hydroxide in adesiccator. Melting point 95- 97 C. Analysis:

Calculated Found from formula Percent Carbon 53. 8 53. 6 PercentHydrogen 9.0 9. 0' Percent Nitrogen 11. 1 11. 4

The sulfenamides produced in accordance with Ex amples 1 and 2 weretested as rubber vulcanization accelerators in the following naturalrubber tire tread formula, in which all parts are given by weight:

Formula I Rubber Q 100 HAF Carbon black 50 Zinc oxide 3 Softener 3Stearic acid 2.6 Antioxidant 1.8 Sulfur 2.6 Accelerator 0.5

Four rubber compositions, were mixed in a conven-, tional manner, inaccordance with Formula I, 'to providevulcanizable compositionsdilfering only in the accelerator employed. Two test accelerators werethose produced according to Example 1 and 2, another was the commercialaccelerator Z-mercaptothiazoline; and the fourth composition was a blankcontaining no accelerator. Separate portions of the four compositionswere heated at 280 F. for 30, 60, and 90 minutes, and the vulcanizedcompositions so produced were found to possess the fol- The above test.ien1onstrates that the accelerators of,

TABLE 2 Mooney Scorch Acceleratorat 250 F minutes2-lviercaptothiazoiine. .13 Example 1 Example 2 21 The accelerators ofthe invention were also tested against 2-mercaptothiazoline and a blankin a synthetic rubber tire tread formula. The rubber in this case wasthe standard low temperature butadiene-styrene U. 8. Government rubberZ-369, containing 1.25% of antioxidant. The formula was as follows:

Formula II Synthetic, rubber 100 HAF carbon black 48 Processing oil Zincoxide Sulfur Stearic acid Antioxidant 0 Accelerator -4 1 Thecompositions were mixed as before and vulcanized by heating at 280 F.for 30, 60, and 90 minutes. Physical properties; of the vulcanizates arein Table 3.

i bnowwoo TABLE 3 Modulus at 300% Tensile Strength at elongation in p.s. i. break in p. s. i. Accelerator (Cure in minutes) 30 6O 90 None 200275 150 200 550 z-Mercaptothiazoiinet 875 1, 975 2. 300 2, 800 3, 00 3,425 Example 1 1, 200 2,075 2, 350 3, 400 3, 700 3, 500 Example 2 675 l,700 2, 050 2, 425 3, 625 3, 050

The above tests show that the accelerators of the invention areexcellent vulcanization accelerators in synthetic rubber. Vulcanizatesof the three compositions produced in the presence of accelerators wereaged for 2 days inan oven at 212 F. Physical properties of the agedcompositions are shown in Table 4.

, Thus the new accelerators, provide synthetic rubber vulcanizatesdisplaying excellent aging properties.

The invention comprehends the acceleration of sulfur vulcanizationwhether the sulfur is present in the rubber composition as free sulfuror chemically bound sulfur available for vulcanization as may beprovided by the socalled sulfur donors. Examples of a few known sulfurdonors are the following substances:

Tetrarnethylthiuram disulfide Polysulfides of phenols and cresolsDiethyl xanthogen disulfide Polyethylene polysulfides The acceleratorsof the invention are usually employed in the range of 0.5 to 2.0% byWeight of the rubber in the vulcanizable composition, but they areuseful in the broader range of 0.1 to 10%. Since the new acceleratorsare very efilcient at the ordinary vulcanizing temperatures of 250-400F., they do not require further activation for most purposes. However,they may be used in combination with one or more additional conventionalaccelerators and/ or activators to provide specialvulcanizablecompositions displaying unusually rapid or critical vulcanizingproperties and to produce vulcanizates exhibiting superior physical andchemical properties desired for special applications.

What is claimed is:

l. A vulcanizable composition including rubber, sulfur and a smallamount of N-tert-butyl-thiazoline-Z-sulfen-' amide.'

2. A process of vulcanizing rubber including heating a mixture ofrubber, sulfur and a small amount ofN-tertbutyl-thiazoline-Z-sulfenamide.

3. A vulcanizable composition including rubber, sulfur and a smallamount of N-tt-octyl-thiazoline-Z-sulfenamide.

4. A process of vulcanizing rubber including heating a mixture ofrubber, sulfur and a small amount of N-ttoctyl-thiazoline-Z-sulfenamide.

5. A vuleanizable composition including rubber, sulfur and a smallamount of a substance having the formula wherein R is a tertiary alkylradical containing 4 to 12 carbon atoms, inclusive.

6. Process of vulcanizing rubber including heating a mixture of rubber,sulfur and a small amount of a substance of the formula CHz- S wherein Ris atertiary alkyl radical containing 4 to 12 carbon atoms, inclusive.

References Cited in the file of this patent UNITED STATES PATENTS Re.19,286 'Zaucker Aug. 21,1934 2,321,305 Messer June 8, 1943 2,339,002Cooper Jan. 11, 1944 2,419,283 Paul Apr. 22, 1947 2,445,722 Carr et alJuly 20, 1948 2,700,659 Carr Jan. 25, 1955

1. A VULCANIZABLE COMPOSITION INCLUDING RUBBER, SULFUR AND A SMALLAMOUNT OF N-TERT-BUTYL-THIAZOLINE-2-SULFENAMIDE.